1. Field of the Invention
The present invention relates to an apparatus for reducing an exciting force applied to a building by an earthquake. More specifically, the present invention relates to a damping device for cancelling an exciting force by actively generating a force.
2. Description of the Related Art
Passive seismic isolators (structure) and active damping devices are employed for preventing the collapse of a building structure caused by the exciting force of an earthquake. A passive seismic isolator, is composed of a damping material, such as laminated rubber sheets or the like interposed between a building structure and the earth surface to prevent the horizontal exciting force resulting from an earthquake from being directly applied to the building structure. Such a device is simple in construction and excellent in performance. However, since the apparatus must be inserted between the building structure and the foundation (earth surface), it is difficult to apply the apparatus to existing building structures, although it is applicable to new building structures.
An active damping device includes an artificial vibrator installed in a building structure. An acceleration caused by an earthquake is sensed by a sensor, the direction in which the building structure is vibrated is calculated by a computer and an exciting force in the direction for cancelling the vibration of the building structure is generated by the vibrator to thereby reduce the vibration. This apparatus is also applicable to an existing building structure. The vibrator generates the exciting force by swinging a large weight by a motor or rotating an eccentric weight. Thus, the damping device has a problem that a certain period of time is needed before the cancelling exciting force is generated. In particular, since an earthquake called a shallow earthquake causes large vibration without any previous notice, an exciting force is applied to a building structure before the damping device is operated.
An object of the present invention is to provide a damping device applicable to an existing building structure and capable of coping with a sudden exciting force resulting from, for example, an earthquake with a vertical shock.